Transformer thermal protector



March s, 1938.

' L. F. YOUNG TRANSFORMER THERMAL PROTECTOR Filed July 7. 1956 3 Sheets-Sheet l Inventor Iewfl F Fa m 1 and 64 g A ltomgy March 8, 1938.

] nvenlor lewd? and I g llomcy March 8, 1938. YOUNG 2,110,639

TRANSFORMER THERMAL PROTECTOR Filed July 7, 1936 5 Sheets-Sheet 3 2 :11] 37 #5 o o i t o fi I 4 #2 I 37 46 47 7 7 Inueniar UNITED STATES PATENT OFFICE TRANSFORMER THERMAL PROTECTOR Lewis F. Young, Ketchikan, Territory of Alaska Application July 7, 1936, Serial No. 89,366

2 Claims.

This invention is a device for protecting distribution and power transformers from damage arising as a result of an overload; and an important object of the present invention is to improve upon. the present practices now prevailing in the art for so protecting a transformer.

As is Well known one of these practices consists in installing fuses in primary or secondary circuits of transformers, which, when the fuse capacity is reached, melt and disconnect either the transformer from its source of supply or the load from the transformer, which necessitates the sending of a man to re-fuse the transformer; and the other practice which consists in installing fuses of a capacity to take care of a momentary overload of 75 or 100 per cent, should a continuous overload of 50 per cent develop, the fuse under such circumstances would not blow and the transformer would overheat and burn out with a consequent considerable repair cost to the power company as well as a lengthy delay to the customers, this delay being caused by, and

being incident to the time required for changing the transformer. 25 In accordance with the present invention, however, means is provided for use in connection with the transformer as will permit the transformer to carry high momentary overload and yet trip before any serious damage is caused by prolonged overload.

The invention together with its objects and advantages will be best understood from a study of the following description taken in connection with the accompanying drawings wherein:

' Figure 1 is a detail view taken through the type of switch wired in circuit with a transformer and embodying the features of the present invention.

Figure 2 is an end elevational view of a transformer tank also illustrating the invention.

Figure 3 is a vertical sectional, elevational view through the switch.

Figure 4 is a detail sectional elevational view showing the spring which serves to normally urge the switch toward open position.

Figure 5 is a diagrammatic view of a modification of the invention employing a fiat bi-metal flexible strip at the oil switch in conjunction with hollow bi-metal expansible diapraghm members 50 within the transformer.

Figure 6 is a similar view of another form of the invention wherein a thrust producing screw is used in conjunction with helical thermal members, and

" Figure '7 is a similar view of still another form of the invention in which a fluid expansible member, a spiral Bourdon tube and a helical thermal member are combined with a thrust producing screw for effecting release of the switch latch.

Referring in detail to the drawings, it will be seen that 5 indicates generally the type of oil switch which is suitably wired in circuit with the transformer, and which includes among other parts a casing 6 that is adapted to contain oil to an appropriate level, as for example a level 10 suggested by broken line in the drawings and indicated by the reference numeral 1.

Suitably journaled in the casing is a shaft 8 provided at one end with a suitable handle 9 for use in manually closing the switch. 5

Also suitably mounted within the casing are conventional contact assemblies ID with which cooperate a contact blade ll carried by an arm I2 that has an end accommodated within a notch [3 provided in a make and break wheel 0 mounted on the shaft 8 to rotate therewith. Plate II is normally urged into engagement with the contact assemblies l8 through the medium of a spring l5 secured at one end to the arm l2 and at a relatively opposite end to the wheel It.

Normally urging the shaft 8 to rotate in one direction for moving the blade I I out of engagement with the contact assemblies I0 is a suitable spring I6 that is disposed about the shaft 8 at one end and is secured at one end to the shaft and at a relatively opposite end to the adjacent wall of the casing 6 as will be clear from a study of Figures 3 and 4.

In accordance with the present invention the oil switch just described is characterized by having mounted in the casing 6 thereof in any suitable manner and adjacent one end of the casing a latch housing H in which operates a spring projected plunger I8 normally urged to a projected position through the medium of a spring 0 [9. On one end of the shaft 8 there is provided a cam 20 formed with a shoulder 30 in the path of which a roller-equipped end of the latch rod l8 normally extends to engage the shoulder for holding the shaft 8 and associated parts against rotation in opposition to spring l6 so that the switch is normally in a closed position.

For manually retracting the latch bar [8 there is provided a control rod 2| that operates in a suitable opening provided in one wall of the casing 6 and at its outer end equipped with a knob 22. At its inner end the rod 2| is pivotally connected to a link 23 which intermediate its ends is pivoted to a bracket 24 mounted on the guide housing I'I. At its other end the link 23 is pivoted to the latch rod it. Thus it will be seen that by pushing in on the button 22 latch rod l8 will be retracted against the action of spring l9 and out of engagement with the shoulder 39 of cam 28 permitting the shaft 8 and associated parts, under influence of spring E6 to rotate for moving the switch plate ll out of engagement with the switch contact assemblies ill for opening the switch. Further in accordance with the present invention means is provided for tripping the switch 5 automatically, that is to say, for retracting the latch E8 to permit the switch to move to open position, such means consisting broadly of an external thermal element operated by the temperature of the transformer oil above ambient temperature.

In the form of the invention shown in Figures l and 2 there is suitably secured at one end thereof to a bracket 28 within the switch casing 6 a compensating strip 29 of bi-metal which extends a few inches below the normal oil level. The free end of the thermal element of the transformer tank is connected with the free end of the compensating strip 29 of the oil switch casing through the medium of a wire 31 protected by a suitable sheathing 32.

Also intermediate its ends, strip 29 is suitably connected with the latch l8 through the medium of rods 33 and 33', which are joined as at 42 by a swivel connection. The thermal element 25 is designed to act at a predetermined temperature rise of the transformer cooling oil over the temperature of the switch cooling oil and the thermal element 29 is designed to compensate for changes in temperature of the oil switch, the differential in the relative action of the thermal elements being set for 20 degrees, degrees, 40 degrees, or 50 degrees as desired. As the temperature of the switch oil varies, the compensating strip 29 will be flexed to move the main thermal element 25 toward or away from the tank wall of the transformer without withdrawing the roller latch from under the depth or shoulder of the cam and thereby maintain the critical or temperature differential at which the device is set to operate.

From the above it will be apparent that as the transformer temperature increases the thermal strip 25 will fiex away from the adjacent wall of the tank of the transformer thus exerting a pull on the wire 3!. This pull will be transmitted to the compensating strip 29 to such an extent that when the critical temperature differ ential is reached the latter will be flexed in a manner to draw the latch rod [3 against the action of spring 19 out of engagement with the shoulder 3% of cam at. In this manner shaft 8 an associated parts will be free to rotate under action of spring 56 for opening the switch to prevent damaging or burning out of the transformer.

Obviously to reset the switch all that is necessary is to rotate the shaft 8 manually by gripping the handle 8 and in a direction reverse to the action of the spring E6 until the shoulder 39 is engaged with the projected latch l8 which latch it will return to its projected position under action of spring l9 as the thermal element 25 cools.

In the form of the invention shown in Figure 5 instead of employing a thermal element such as the element 25 shown in Figure 2 there may be substituted therefor a plurality of pairs of bi-metallic strips 34 the strips of each pair being secured together at their respective opposite ends as at 35 and the strips of the pairs provided with openings therethrough for receiving one end of the rod 36 that connects the strips 34 with the aforementioned compensating bimetallic strip 29. Thus it will be seen that the strips 34 will have an expansive action relative to one another upon an increase in the temperature of the transformer above ambient temperature so as to exert a pull on the rod 36 for retracting the latch bar l8 to trip the switch 5 when the critical temperature difference is reached.

In the form of the invention shown in Figure 6 in lieu of the compensating strip 28 there is provided a bi-metallic helix compensator 31 formed integral with the inner end of the rod 38 and connected at one end with a thrust producing screw 39 threaded through a block 40 suitably mounted within the switch casing ii and which screw 39 has a reduced end 4! swivelly connected as at 42 with a rod section 43 that is suitably associated with the latch bar 18.

Also in this form of the invention there is suitably associated with the end of the rod 38 terminating within the transformer tank 21 a bimetallic helix 44.

It will be apparent that the helix 44 will expand in response to an increase of temperature in the tank of the transformer and when so expanding will exert a turnin action on the rod 38 causing the screw 35] to thread through the block 4@ in a manner to exert a pull on the latch bar l8 for retracting it to permit the switch to move to an open position to prevent damaging or burning out the transformer as the result of an overload thereon.

In the form of the invention shown in Figure 7 the compensating helix 3! is suitably connected with a spiral Bourdon tube 45 that is connected through the medium of tubing 46 with a bulb 4! containing an expansive medium and which is of course suitably mounted within the transformer tank. The helix El, screws 39, and Bourdon tube 45 are housed in the oil switch casing. Thus as the medium in the bulb 4'! expands in response to a temperature increase in the transformer tank the Bourdon tube 45 will expand for transmitting a rotative movement to the screw 39 through the helix 3'! for threading the screw 39 outwardly and in a direction to exert a pull on the latch bar 58 for retracting the latter to permit the switch to be opened by the spring 56.

Thus it will be seen that any one of several different types of thermal or heat responsive means may be connected with the latch 13 for retracting the latter to free the switch to permit the latter to move to an open position when the critical temperature difference is reached within the transformer to the end that while provision is made to prevent damaging or burning out the transformer momentary overload may be carried by the transformer, while at the same time provision is made for tripping the switch to cut out the transformer before any serious damage can result as might otherwise be caused by prolonged overload when overload fusing is resorted to.

The above device is applicable to all transformers whether already installed or on new ones, permitting maximum output of the equip ment to be utilized without fear of burnouts.

Having thus described the invention what is claimed as new is:--

1. For use in protecting a transformer against overloading, an oil switch including fixed contacts and a blade movable into and out of engagement with said fixed contacts, a shaft, means for supporting the blade from the shaft for turning movement with the shaft, spring means engaged with the shaft for normally urging the same to rotate in one direction for moving the switch blade out of engagement with the contacts, a cam member on said shaft, a latch mounted within the casing of the switch, and including a spring projected latch bar normally engaging the cam and cooperating therewith for retarding rotative movement of the shaft in opposition to said spring for normally holding the switch in closed position, thermal means adapted to be connected with a transformer and operatively connected with said latch rod for retracting the rod at a predetermined temperature rise of the transformer oil over the temperature of the switch oil, and thermal means acting oppositely against the first thermal means in response to variations in the temperature of the switch oil.

2. Apparatus for protecting a transformer against overload including an oil switch embodying fixed contacts and a movable contact, the latter normally engaging the fixed contacts and movable to disengaging position, latch mechanism for retaining the movable contact in engaging position and including a latch bar retractable to unlatching position, thermal means adapted to be connected to a transformer and operatively connected to said latch bar for retracting said bar at a predetermined temperature rise of the transformer oil over the temperature of the switch oil, and thermal means acting oppositely against the first thermal means in response to variations in the temperature of the switch oil.

LEWIS F. YOUNG. 

